This invention is generally directed to toner compositions that are pressure sensitive, and more specifically the present invention is directed to toner compositions containing blends of two or more immiscible polymers, which compositions are very useful in causing the development of images in electrostatographic imaging systems wherein pressure fixing, especially pressure fixing without the pressure of heat, is employed. In one embodiment the toner compositions of the present invention are comprised of a blend of two immiscible polymers, and a plasticizer.
The development of electrostatographic images, and in particular, electrostatic images utilizing developer compositions containing toner materials is well known. In these systems, an electrostatic latent image is formed on a photoconductive member, and the image is developed with a toner composition comprised of resin particles and carbon black. Subsequently the developed image is transferred to a suitable substrate, where fixing is accomplished by heat. Thus, final copies of the toner image are produced by heating the toner to a temperature at which the toner particles begin to flow in order to effect fusing of the particles to a support substrate, such as paper. Such a fixing process generally requires substantial amounts of energy, and prior to producing the first copy in a machine employing heat pressure fix systems, it is necessary to allow the machine to reach an appropriate temperature in order that the first copy can be fused properly. Other fixing systems are known including radiant fusing, vapor pressure fusing, pressure fusing, a combination of pressure heat fusing systems, and the like.
Cold pressure fusing has a number of advantages, primarily relating to the requirement for less energy, since the toner compositions involved can be fixed at room temperature. Nevertheless, many toner compositions used in prior art cold pressure fixing systems suffer from a number of deficiencies. For example, these toner compositions must usually be fused under high pressures, which pressures have a tendency to severely disrupt the toner fusing characteristics of the compositions employed. This results in images of low resolution, or no images whatsoever, and in some of these systems, substantial image smearing has been noticed because of the high pressures required. While attempts have been made to improve toner compositions for cold pressure fix systems, such compositions in many instances have a number of undesirable characteristics, including agglomeration of particles at room temperature, insufficient flowability under high pressures, lack of adhesion to the support substrate, such as paper, unsuitable blocking temperatures, and an insufficient brittleness to allow preparation of such materials by, for example, known commercial jetting methods, or known fluid energy milling processes.
Accordingly, there continues to be a need for improved toner compositions for use in imaging systems utilizing cold pressure fixing processes. More specifically, there is a need for cold pressure fix toner compositions which exhibit excellent flowability at high pressures, adhere to the substrate on which the image is to be permanently fixed, such as plain bond paper, have suitable blocking temperatures, and are of sufficient brittleness to allow comminution, utilizing known jetting processes, or fluid energy mills.